Hitherto, cell structures a having cavity in the form of being bored in the direction of central axis (for example, honeycomb structures) have been used for various uses. For example, there is disclosed an adsorption-device which has a bypass mechanism for internal combustion engines and which has such a construction that at the time of cold starting, hydrocarbons contained in an exhaust gas from internal combustion engines (for example, automobiles) are adsorbed to an adsorptive material supported on cell partition walls by passing the gas through a cell portion of a honeycomb structure, and thereafter the gas is led to a catalyst in the state of low reactivity to diminish the burden, and after warming up, the flow path of the gas is changed to the hollows of the honeycomb structure to lead the gas to a catalyst in the state of the reactivity being increased (U.S. Pat. No. 5,315,824).
Furthermore, an adsorptive body for purification of exhaust gas in which a well portion for blowing of gas in order to secure gas passage (for blowing of exhaust gas therethrough) is formed in a honeycomb structure is disclosed (JP-A-7-232084).
Moreover, an apparatus in which another structure (catalyst converter) is provided in a hollow pore is disclosed (German Patent DE19502345A1).
A holding structure for a heat storage body in which a fuel nozzle is disposed in a central cavity of a cylindrical honeycomb heat storage body as a heat exchanger (JP-A-11-211371).
Further, there is disclosed a rotary switching single type regenerative burner in which a burner is provided in a central cavity of a honeycomb heat storage body whereby the heat storing portion and the burner portion are integrated(“Energy Saving”, Vol. 48, No. 10, 1996; title “rotary switching single type regenerative burner”).
As a reformer for fuel cells, etc., there is disclosed a fuel reformation apparatus according to which a gas is passed through a doughnut-shaped catalyst portion and then the gas is passed through the inner hollow portion of the doughnut-shaped catalyst portion (JP-A-8-67502).
Furthermore, there is disclosed a hydrogen purification apparatus in which a reaction chamber is provided at outer periphery of a tubular reformed gas flow path, a honeycomb catalyst body is provided inside the reaction chamber, and a heat exchanging fin is provided on the wall surface of the reformed gas flow path which contacts with the downstream side of the catalyst body (JP-A-2000-44204).
As mentioned above, cavities formed in honeycomb structures used for the above uses have important roles to perform a function as a bypass for heat, a function of accelerating rise of temperature of catalyst, a function of holding other structures, and the like.
However, it has become clear that as shown in FIG. 50, when an isostatic pressure F is externally applied to the outer peripheral surface of a honeycomb structure 100 having a cavity, and the pressure externally applied to the outer surface F reaches a certain value, there occurs a peculiar phenomenon that the honeycomb structure is broken in such a manner that the inner side portion as shown by a dotted line in FIG. 50 falls into the cavity. Thus, the conventional cell structures have a problem in isostatic breaking strength for holding the structure in a container while securing sufficient reliability in endurance.
Furthermore, in the case of sealing the cavity against passing of fluid through cells which are flow paths, the periphery of the cavity is demanded to have such a mechanical strength as endurable against sealing force and besides it is demanded to secure a sufficient sealing face. However, the conventional cell structures cannot sufficiently meet these demands. That is, sealing is generally carried out by pressing a sealing member to the inner peripheral surface of the cavity at the end face of the cell structure, but in this case the section of the partition wall constituting the cell is a sealing face, and sufficient sealing cannot be performed because the sealing member linearly contacts with the sealing face. Moreover, sealing force is received only by the partition wall and hence no sufficient pressure can be externally applied to the outer peripheral surface due to the restriction in mechanical strength. In such a case, the direction of flow path of fluid through the cells around the cavity or compressive strength of the cell structure in the direction of central axis is important, and it is necessary to design a honeycomb structure so as to give a proper compressive strength in this direction.